1. Field of the Invention
The present invention relates to a liquid crystal display device, and in particular relates to a liquid crystal display device with a unitary optical film.
2. Description of the Related Art
Liquid crystal display devices are already widely used in all kinds of electronic devices, such as LCD TVs and computers. Key advantages are low electricity consumption, low driving voltage, and the possibility of achieving lighter weight and thinner volume. However, the liquid crystal display panel in the liquid crystal display device cannot emit light by itself, and has to pair with a back light unit to light the screen evenly.
Please refer to FIG. 1. FIG. 1 shows a side view of the conventional liquid crystal display device 1 utilizing an edge-light type back light unit. The liquid crystal panel module 40 is disposed in front of the back light unit 10, wherein the back light unit comprises: a light-emitting unit 11, a light guide panel 12, a lower diffusion plate 13, a prism sheet 14, and an upper diffusion plate 15.
The light guide panel 12 guides the light beam emitted from the light-emitting unit 11 to the lower diffusion plate 13. The lower diffusion plate 13 then disperses and hazes the light beam coming from the light guide panel 12 and distributes the brightness evenly. Nevertheless, the brightness within the effective viewing angle is reduced drastically due to the lower diffusion plate 13.
In order to solve this problem, the prism sheet 14 receives the light beam that passes through the lower diffusion plate 13 and converges the emergent angle of the incident light beam to strengthen brightness within the effective viewing angle. The prism sheet 14 is a commonly sold brightness enhancement film, with a 90° apex angle, and prism sheet 14 curving towards the liquid crystal panel module 40.
Finally, the light beam is dispersed and hazed again through the upper diffusion plate 15 in order to provide a uniform light beam to the liquid crystal panel module 40 situated in front.
However, the above-mentioned back light unit needs at least three individually manufactured optical films, each requiring its own substrate material, which yield a high production cost.
Furthermore, the air layer formed between the upper diffusion plate and the prism sheet will cause a portion of the light beam to fully reflect from the prism sheet and render it unable to be projected into the upper diffusion plate. The strength of the light beam will be consumed with the increased length thus weakening the overall brightness. Conventionally, in order to increase the brightness of the back light unit it is necessary to raise the light source power of the light-emitting element, but this also means accelerated energy consumption.
In this regard, a liquid crystal display device with a unitary optical film came into high demand.